This invention relates generally to electronically controlled fuel injection systems and, more particularly, to a method and apparatus for delivering multiple fuel injections to the cylinder of an internal combustion engine during a fuel injection event including a post fuel injection, based upon engine operating conditions.
Electronically controlled direct fuel injection devices such as electronically controlled fuel injectors are well known in the art including both hydraulically actuated electronically controlled fuel injectors as well as mechanically actuated electronically controlled fuel injectors. Electronically controlled fuel injectors typically inject fuel into a specific engine cylinder as a function of an electronic fuel injection signal received from an electronic fuel injection control device (controller). These signals include waveforms that are indicative of a desired injection rate as well as the desired timing and quantity of fuel to be injected into the cylinders.
Emission regulations pertaining to engine exhaust emissions are becoming consistently more restrictive throughout the world including, for example, restrictions on the emission of hydrocarbons (HC), carbon monoxide, the release of particulates, and the release of nitrogen oxides (NOx). Tailoring the number of injections and the injection rate of fuel to a combustion chamber, as well as the quantity and timing of such fuel injections, is one way in which to control emissions and meet such emission standards. As a result, split or multiple fuel injection techniques have been utilized to modify the burn characteristics of the combustion process in an attempt to reduce emission and noise levels. Split injection typically involves splitting the total fuel delivery to the cylinder during a particular injection event into at least two separate fuel injections such as a pilot injection and a primary fuel injection which might further include a main injection and an anchor injection.
As part of an emissions control strategy it has been found to be beneficial to inject a xe2x80x9cshotxe2x80x9d of fuel into a fuel cylinder later in the exhaust stroke. Such a later xe2x80x9cshotxe2x80x9d is referred to as a xe2x80x9cpost shot,xe2x80x9d or xe2x80x9cpost injection.xe2x80x9d The post shot is injected to provide unburned hydrocarbons to a NOx catalyst for higher NOx conversion efficiency.
To additionally effectively reduce NOx emissions it is known in the art to include an exhaust treatment device including a NOx catalyst in an exhaust system of an internal combustion engine. In a lean burning direct injected compression ignition engine a variety of NOx catalysts may be used. However, the current technology of NOx catalysts requires a sufficient concentration of a reducing agent, usually a hydrocarbon (HC) compound, to be present in the exhaust gas at the catalyst. Therefore, the reducing agent or hydrocarbon must be introduced into the exhaust in order to achieve an efficient reduction in NOx emissions. In order for the NOx catalyst to be properly activated and for efficient reduction of NOx levels to occur, the catalyst must also achieve a proper operating temperature.
A variety of different methods of heating an exhaust catalyst have been developed. The simplest of these involves including a separate heating element in the vicinity of the catalyst. Unfortunately, the direct heating of the catalyst in this fashion substantially increases both electrical and exhaust system complexities and costs while failing to achieve optimum activation of the catalyst. Previous secondary injection systems which inject additional fuel into the engine to create additional heating of the exhaust have failed to take into account the effects of secondary injections on fuel economy, engine durability, injector durability and fuel dilution of engine oil.
At different engine operating conditions, it may be necessary to use different injection strategies in order to achieve both desired engine operation and emissions control. As used throughout this disclosure, an xe2x80x9cinjection eventxe2x80x9d is defined as the injections that occur in a particular cylinder or combustion chamber during one cycle of the engine (xe2x80x9ccylinder cyclexe2x80x9d). For example, one cycle of a four stroke engine for a particular cylinder, includes an intake, compression, expansion, and exhaust stroke. Therefore, the injection event/cylinder cycle in a four stroke engine includes the number of injections, or shots, that occur in a cylinder during the four strokes of the piston. As used in the art, and throughout this disclosure, an xe2x80x9cengine operating cyclexe2x80x9d includes the individual cylinder cycles for the cylinders included therein. For example, an engine operating cycle for a six cylinder engine will include six individual cylinder cycles, one for each of the cylinders of the engine (with each cylinder cycle having four strokes, for a total of 24 strokes). Generally, the cylinder cycles overlap, so that the beginning of the next successive cylinder cycle of a particular cylinder might begin prior to the completion of the beginning of the next engine operating cycle. The term xe2x80x9cshotxe2x80x9d as used in the art may also refer to the actual fuel injection or to the command electronic fuel injection current signal (electronic fuel injection current signal), also referred to simply as a fuel injection signal, to a direct fuel injection device, fuel injector or other fuel actuation device indicative of an injection or delivery of fuel to the engine.
In the past, some prior catalyst activation systems have provided heated exhaust gasses to an exhaust catalyst using secondary fuel injections, such as the method disclosed in the U.S. Pat. No. 5,479,775 to Kraemer et al., where a secondary fuel injection is provided and the fuel is combusted to heat the exhaust gasses which are in turn supplied to an exhaust catalyst. The ""775 patent does not control secondary fuel injection in order to address issues related to engine durability and fuel economy. Similarly, U.S. Pat. No. 5,839,275 to Hirota et al., describes an exhaust system catalyst and the use of an additional sub-fuel injection between a first and a third fuel injection, which increases exhaust gas temperature. However, neither the ""775 patent or the ""275 patent particularly address varying such a secondary (sub) injection to improve emissions, improve engine and injector durability and improve fuel economy. Nor do the ""775 and ""275 patents address introducing such a secondary injection gradually in order to alleviate torque/mechanical energy produced by such an injection, which may cause problems in governing fuel and/or engine speed.
Under the more restrictive emissions regulations of today, these prior fuel partitioning strategies may yield higher than desirable hydrocarbon emissions, excess fuel consumption, excessive engine wear, reduced injector life and excessive fuel dilution of the oil. Even with more advanced electronically controlled injectors, during certain engine operating conditions, it is sometimes difficult to accurately control fuel delivery, even when utilizing electronic fuel injection current control signals.
Desired engine performance is not always achieved at all engine speeds and engine load conditions using the previously known fuel injection strategies. Based upon engine operating conditions, the injection timing, fuel flow rate and the injected fuel volume are determined in order to reduce emissions and improve fuel consumption. This is not always achieved in a split injection system or with a post injection due to a variety of reasons, including limitations on the different types of achievable electronic fuel injection signal waveforms, the amount of fuel injected during the primary shot, when the two injections take place during the particular injection event, the timing sequence between the two injections and the temperature of the exhaust catalyst. As a result, problems such as injecting fuel at a rate or time other than desired within a given injection event and/or allowing fuel to be injected beyond a desired stopping point can adversely affect emission outputs and fuel economy.
Accordingly, the present invention is directed to overcoming one or more of the problems as set forth above.
In one aspect of the present invention there is disclosed an exhaust gas heating system of a direct injection compression ignition internal combustion engine which has a plurality of combustion chambers and an exhaust passage, and one or more direct fuel injection devices, each operable to inject fuel directly into a corresponding one of the combustion chambers. The system also includes a fuel injection controller which is operable to provide to at least one of the direct fuel injection devices, a post fuel injection signal during a corresponding cylinder cycle of the corresponding one of the plurality of combustion chambers. The post fuel injection signal is timed so as to provide exhaust gas heating from a resultant post fuel injection, and the fuel injection controller dynamically determines the particular one or more of the plurality of direct fuel injection devices to which the post fuel injection signal will be applied based on a temperature related engine operating parameter.
The post fuel injection may also be timed and/or shaped such that it does not produce a substantial amount of mechanical energy but instead produces heated exhaust gasses.
These and other aspects and advantages of the present invention will become apparent upon reading the detailed description in connection with the drawings and appended claims.